How do I get a list of all companies who have NOT ordered a particular product?

Let's get the list you want in QuickBooks Online (QBO), @HTF.

In QBO, reports give you a snapshot of different areas of your business. For the time being, there's no specific one that'll provide the list of all companies who haven't ordered a particular product. However, you can pull up a sales or transaction report (i.e., Sales by Customer Detail, Sales by Product/Service Detail, or Transaction List by Customer) from the Reports menu and filter the product name. Then, manually check the companies that aren't included on the list. They're the ones who haven't ordered the product for that specific time frame. Here's how:

1. Go to the Reports menu.
2. Pull up the report you want (i.e., Sales by Customer Detail).
3. Click the Customize button.
4. Set the Report period.
5. Go to the Filter section and choose the particular product in the Product/Service field.
6. Select Run report. 

Once you're done, export the report to an Excel file. From there, manually check (i.e., adding a customer column) the companies who haven't ordered a particular product from your business. You can refer to this article for the detailed steps: Export your reports to Excel from QuickBooks Online.

Also, to see the complete list of available reports for your version of QBO and how you can get the most out of them, I'd recommend checking out these articles:

• Reports included in your QuickBooks Online subscription
• Customize reports in QuickBooks Online

Please don't hesitate to keep me posted on how it goes in the comments below. If you have other reporting concerns and questions about managing your sales and product list in QBO, I'll gladly help. Take care, and I wish you continued success, @HTF.